At present, several typologies of cooking tops are available on the market, the most widespread typology using one or more gas burners, wherein the amount of heat necessary for cooking food is generated through combustion of a gas appropriately mixed with air.
Systems of burners are also known in the art, which have a substantially circular shape and have two concentric burners, typically an outer burner and an inner burner.
Such systems of burners are known as “double-crown”, and have gas supply means, said supply means having a pair of gas inlet ducts associated with independent control valves, so that the two burners (i.e. the outer burner and the inner burner) can be used either together or separately in order to achieve good variability and a homogeneous distribution of the heat to be supplied to the cooking containers. As an alternative, both concentric burners may be fed by a single gas inlet duct, with an associated tap, which simultaneously feeds the different intake channels that supply the air-gas mixture to the concentric burners.
Such systems of burners further include a cup having at least one first chamber for supplying the air-gas mixture to the inner burner and at least one second chamber for supplying said air-gas mixture to the outer burner, said cup being associated with the supply means and with at least one flame divider (or cap).
The flame divider is positioned on the cooking top where the system of burners is installed, and uses the air under or above the cooking top as primary air to be mixed with the gas.
Also, the cup is usually made of die-cast aluminum, while the flame divider or cap is usually made of enameled cast iron (or brass alloy or steel) and acts as a cup closing element.
The systems of burners known in the art typically propagate a flame known as “crown flame”; a “crown flame” is a flame with a substantially radial direction of propagation, i.e., a flame that propagates outwards from the gas burner in a substantially radial direction with respect to the burner axis, and therefore in a direction which is substantially tangential to a visible surface of the cooking top. Said “crown flame”, when emitted at an insufficient height above the cooking top, may cause the generation of a high level of CO, NO and CO2 because of poor supply of secondary air, necessary for a proper combustion, towards the flames.
In atmospheric burners, i.e. burners wherein primary air is mixed with gas at atmospheric pressure, it is almost impossible to achieve stoichiometric values of primary air supply.
The lack of primary air must be compensated for by supplying secondary air towards the flames in order to ensure a complete combustion, resulting in values of CO, CO2 and NOx emissions compliant with the gas regulations currently in force.
Single burners are also known in the art which include a flame divider or cap having a plurality of apertures adapted to generate a “carpet flame”, i.e., a flame that propagates out of the system of burners in a substantially axial direction with respect to the axis of the system of burners, and therefore in a direction which is substantially orthogonal to a visible surface of the cooking top.
A carpet flame may be a total carpet flame or a perimetric carpet flame, depending on whether it covers a geometric figure (generally a circle) entirely or just the peripheral portion of said geometric figure (generally a circular crown).
Also in the case of a perimetric carpet flame, a plurality of concentric rows of apertures may be provided and adapted to generate a “carpet flame”, in particular for the purpose of also heating the central portion of the base of a cooking vessel positioned over the gas burner.
However, the solutions known in the art suffer from a few drawbacks.
In particular, in the solutions currently known in the art, “double-crown” systems of burners include a gas inlet duct centrally coupled to the outer burner; this type of coupling results in the primary air-gas mixture impacting against the inner wall of the central cup of the inner burner, thus being drastically slowed and suddenly diverted upwards, which may lead to considerable differences in the velocity at which the primary air/gas mixture will exit through the holes of the flame divider in the areas corresponding to this flow.
The solutions known in the art suffer from the drawback that there are zones where the exit velocity of the primary air/gas mixture is different through the various perforated regions of the flame dividers, which may result in “flame lift” phenomena at ignition time.